King Lear: Madness and age (Cam B.)

Throughout the play, Goneril and Regan reference their father's old age as the source of his madness and his incapability of ruling as king. To what extent does age contribute to Lear's madness? Does his age stand alone in representing his actions throughout the play, are his actions a result of a combination of both madness and his old age, or, perhaps, is his madness singular in affecting his radical actions?
Consider the two following passages for discussion:

Act 2 Scene 4, lines 159-176 (pg 107)
"REGAN: I cannot think my sister in the least --> LEAR: ...on my knees I beg That you'll vouchsafe me raiment, bed, and food!"

Act 1 Scene 1, lines 329-355 (pg 27)
"GONERIL: Sister, it is not little I have to say --> GONERIL: We must do something, and i' th' heat."

Feel free to sight other parts of the play that note King Lear's old age.